Magnetic mercury switch



Feb. 24, 1970 J, w, JONES 3,497,837

MAGNETIC- MERCURY SWITCH I I Filed Nov. 6, 1967 s Sheets-Sheet 1 FIE.. IE.

INVENTOR. JAMES W JONES MM TM ATTORNEYS Feb. 24, 1970 j J. w. JONES 3,497,837

MAGNETIC MERCURY SWITCH Filed Nov. 6, 1967 s Sheets-Sheet z INVENTOR JAMES W. JONES BY TM ATTORNEYS Feb. 24, 1970 v J. JONES 3 4 7 MAGNETIC MERCURY SWITCH Filed Nov. 6, 1967 s Sheets-Sheet s FIIE- El MENTOR United States Patent M 3,497,837 MAGNETIC MERCURY SWITCH James W. Jones, Hollister, Califi, assignor to Compac Engineering, Inc., a corporation of California Filed Nov. 6, 1967, Ser. No. 680,650 Int. Cl. H01h 29/02, 29/08 US. Cl. 335-51 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Field of the invention This invention relates to a new and improved magnetic mercury switch which may be used either singly or in gang to form multiple switch keyboards.

DESCRIPTION OF THE PRIOR ART The increasing use of data processing machinery has produced an increasing demand for highly reliable lowcost switches suitable for multiple switch keyboard applications. 4

SUMMARY OF THE INVENTION It is an object of this invention to provide a switch with a minimum number of parts for ease in manufacture, low cost, and high reliability particularly adapted for mass use in keyboard applications. Another object of this invention is to provide a switch with low contact resistance, high current carrying capacity and no contact bounce. According to another aspect of the invention it is intended to provide a mercury switch which may be operated in non-vertical positions and which is substantially unaffected by vibration.

In order to accomplish these results, the present invention contemplates the provision of an elongated-tube of non-magnetic, non-electrically conducting material suitably sealed at each end to enclose a pool of mercury and a ball of magnetic material having a mercury wettable surface to thereby alter the meniscus of the mercury pool upwards along the surface of the ball. Included in the seals at each end of the tube are electrical terminals communicating with the inside of the tube and having mercury wettable surfaces.

The invention further contemplates the provision of magnetic means for moving the ball of magnetic material between two positions such that in one position the ball of magnetic material rests in the pool of mercury at the bottom of the tube in contact with one electrical terminal and such that in the other position the ball is raised to contact the second electrical terminal while contact with the mercury pool is maintained through the alteration upward of the mercury meniscus to provide a mercury to mercury contact between the two electrical terminals. The parts of the assembly are compactly housed in axial relation for multiple switch keyboard applications and key means provided for actuating the magnetic means to move the ball between the two positions.

The invention is further suitable for keyboard applications in eliminating contact bounce, providing information to a manual operator in the form of a slight impact and sound impulse that the switch is closed and contact made, and maintaining contact when the key switch is 3,497,837 Patented Feb. 24, 1970 depressed despite vibration or shaking of the operators finger.

According to another aspect of the invention, motion of the ball of magnetic material upwards in response to the permanent magnet produces momentary contact between the ball and the second electrical terminal while maintaining contact with the pool of mercury below to provide a momentary mercury to mercury contact between the electrical terminals. The magnetic ball then proceeds upward breaking contact with the mercury pool below thereby breaking the mercury to mercury contact between the electric terminals.

Other modifications of the invention including the use of a biasing magnet to permit operation of the switch in other than vertical positions and unaffected by vibration, and mercury tilting switches are hereinafter described.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a multiple switch keyboard utilizing magnetic mercury switches embodying the present invention;

FIG. 2 is a perspective view of a key and switch embodying the present invention and suitable for application in the keyboard illustrated in FIG. 1;

FIG. 3 is a partially exploded view of the key assembly of the switch and key illustrated in FIG. 2;

FIG. 4 is an exploded view of the magnetic mercury switch element of the switch and key illustrated in FIG. 3;

FIG. 5 is a cross sectional view from the side of the magnetic mercury switch and key in assembled form;

FIG. 6 is a cross sectional view from the side of the magnetic mercury switch with the actuator magnet in the closed switch position;

FIG. 7 is a cross sectional view from the side of the magnetic mercury switch with actuator magnet in open switch position, and including a bias magnet for switch operation in a non-vertical position;

FIG. 8 is a cross sectional view from the side of the switch illustrated in FIG. 7 in closed switch position;

FIG. 9 is a cross sectional view from the side of a momentary contact magnetic mercury switch with actuator magnet in the open switch position;

FIG. 10 is a cross sectional view from the side of the momentary contact magnetic mercury switch in FIG. 9 with actuator magnet in the closed switch position during momentary contact;

FIG. 11 is a cross sectional view from the side of the switch illustrated in FIG. 10 after momentary contact is broken;

FIG. 12 is a cross sectional view from the side of a tilting mercury switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a multiple switch keyboard generally comprised of a console 11, keyboard 12, an individual key switch element 13 embodying the present invention. Each key switch element 13 includes generally a housing 31a,

31b, a mercury magnetic switch 14, actuator magnet 15 and a keying assembly including a finger key 16, k washer 19, plunger 17, and return spring 18 as shown in FIGS. 2 and 3.

The magnetic mercury switch 14, more clearly illustrated in FIG. 4 is comprised of an elongated container body 20 made from glass or plastic tubing, sealed at each end with an inwardly projecting cup 21 and 22 of electrically conducting magnetic material such as alloy 52, an alloy of 52% nickel and 48% iron. On the surface of cup 21 facing the inside tube 20 is welded a plug 23 of mercury wettable metal such as nickel. Sealing cup 22 is formed with a hole 24 around the perimeter of which is welded a sealing 'disc 25 so that a plug 26 of mercury wettable metal such as nickel extends through the hole to the inside of tube 20 upon assembly of the switch.

Sealed within the tube 20 is a pool of mercury 27 (not shown in FIGS. 3 and 4) and steel ball 28 plated with a mercury Wettable metal such as nickel. Referring to FIG. 5, the magnetic mercury switch 14 is operated in a generally vertical position so that the pool of mercury 27 is always in contact With nickel plug 26 which forms the first electrical terminal. Steel ball 28 rests partially floating in the pool of mercury out of contact with plug 23 which forms the second electrical terminal. The mercury meniscus is altered upward along the mercury wettable surface of the steel ball 28.

Because the components of the magnetic mercury switch 14 are assembled along a single axis, the switch is particularly adapted for low cost mass manufacture. In assembling the magnetic mercury switch 14, sealing cup 21, with outer diameter comparable to the inner diameter of glass tube 20, is heat sealed inside one of the open ends of the glass tube 20. The cup material is chosen to have a coeflicient of expansion compatible with the tube material. Heat sealing may be localized by infrared heating using a tungsten coil. A nickel plug 23 is welded onto the surface of the sealing cup 21 which faces the inside of the tube. The nickel plated steel ball 28 is then loaded from the other end of the tube in which cup 22 is then heat sealed.

The mercury pool 27 is poured in through hole 24 in cup 22. Disc 25 is then welded to cup 22 sealing the hole so that the nickel plug 26 which is welded to the disc is facing the inside of the glass tube 20. At the time the pool of mercury is poured into the tube, a small amount of mercury inert gas may also be included. The assembled switch is then heated to wet the mercury wettable surfaces with mercury.

The assembled magnetic mercury switch 14 as illustrated in FIGS. and 6 is actuated by an actuator magnet 15 positioned above the switch and movable between two positions. In the upper position illustrated in FIG. 5 the flux of actuator magnet 15 is insufficient to overcome the reluctance of the gap 30 between steel ball 28 and the second electrical terminal 23. As a result the ball rests in the pool of mercury 27 in electrical contact with the first electrical terminal 26 only. The meniscus of the pool of mercury 27 is altered upward along the surface of the ball because of its mercury Wettable surface.

In the lower position shown in FIG. 6, the actuator magnet 15 rests within the cup 21 and draws the steel ball 28 into contact with the second electrical terminal 23 while maintaining the electrical contact with the first electrical terminal 26 because of alteration upwards of the meniscus of mercury pool 27. An efiicient mercury to mercury contact is thereby made between the electrical terminals as illustrated in FIG. 6.

The orientation of magnetic parts is such that the ball is held in contact with the second terminal longer on the up stroke of the actuator magnet than on the down stroke. This renders accidental actuation of the switch, and accidental release of the switch after actuation less likely, when the switch is used by a manual operator.

Because of the shape of the electrical terminals and the moving steel ball, the surfaces of which are all wetted with mercury, and the orientation of the actuator magnet, an electrical circuit is made with low contact resistance, high current carrying capacity and no contact bounce.

Referring to FIGS. 3 and 5, for manually operated pushbutton use, the assembled switch 14 is mounted in the bottom of an elongated plastic housing 31a, 31b, closed at the bottom and including a first electrical outlet 32 from the first electrical terminal 26 through the electrically conducting material of sealing cup 22. Hole 41 is formed in the housing to provide a second electrical outlet 43 from the second electrical terminal 23 through the electrically conducting material of cup 21. The housing 31a, 31b is cylindrical in shape and bisected along a longitudinal axis for easy assembly and includes collars 33 and 34 at each end and an opening 35 in the top. Retainer rings 36 and 37 fit snugly about the collars 33 and 34 when the halves of the housing are assembled together. Keyboard panel boards 38 and 39 shown in phantom in FIG. 5 may further serve to hold the housing together. Longitudinal projections 40 formed along the sides of the longitudinally bisected halves of the housing facilitate joining the two portions.

Positioned axially within the housing and above the magnetic mercury switch 14 is a plunger 17 formed of glass fill nylon in which the actuator magnet 15 made of alnico V is frictionally held. Spring 18 is positioned axially within the housing between the plunger 17 and switch 14 to maintain the actuator magnet 15 in the upper position so that the mercury switch 14 is in a normally open position. Secured to the plunger by an interference fit and projecting outwardly through hole 35 in the housing 31 and in slidable relation therewith is an actuator rod 44 of metal or similar material on which is frictionally fitted a finger key 16 formed of injection molded acrylic plastic.

Return spring 18, formed of stainless steel may be compressed by pushing downward on the finger key 16 to slide the plunger 17 within the housing. Actuator magnet 15 is then moved to the lower position and the steel ball 28 is raised upward to contact the second terminal 23 and close the switch. It is apparent that the coaxial construction and operation of the switch and key make it particularly suited for keyboard application. In keyboard applications upon depression of the switch key, the magnetic ball rises to strike the second electrical terminal producing a slight impact which is transmitted to the operators finger to thereby inform the operator that contact is made. Furthermore, contact is maintained longer on the up stroke than on the down stroke to thereby maintain contact when the switch key is depressed despite vibrations or shaking of the operators finger in the down position.

In the embodiment of the invention heretofore described, the mercury switch is operated in a generally vertical position so that the pool of mercury continually rests upon the first electrical terminal. In a modification of the invention illustrated in FIGS. 7 and 8, a bias magnet 45 is held within the bottom sealing cup 22 so that the switch may be better operated in a non-vertical position at an angle from zero degrees to approximately 75 degrees from the vertical. The bias magnet 45 serves to retain steel ball 28 and mercury pool 27 against the first electrical terminal when the actuator magnet is in its upper position even though the switch is subject to vibration and is at a substantial angle from the vertical as shown in FIG. 7. Depression of the actuator magnet 15 draws the steel ball 28 to contact the second electrical terminal while still maintaining electrical contact through the pool of mercury 27 with the first electrical terminal. The bias magnet serves to render the switch substantially insensitive to vibration even in non-vertical positions and provides sharper switch action.

In data processing equipment it is often desirable to have a momentary contact push button key switch which supplies a single momentary pulse upon depression of the key which actuates the switch. Such a switch eliminates the danger of making multiple electrical contacts by a slip of the finger thereby producing multiple pulses and unwanted multiple signals in the data processing equipment.

According to this embodiment of the invention illustrated in FIGS. 9'11, a section of tubing 46 of glass or other non-magnetic non-electrically conducting material is provided with sealing cups 47 and 48 of electrically conducting magnetic material such as alloy 52 with a coefficient of expansion compatible with the material of the tube. The cups are heat sealed to the inner surface of each end of the tube 46. A plug 50 of mercury wettable material is welded to the surface of cup 48 facing the inside of tube 45. Cup 47 is provided with a hole 51 through the surface communicating with the inside of glass tube 46 and is sealed at the top by a disc 52 of nonmagnetic electrically conducting material welded to the top of cup 47 to form a small chamber at the top of the structure.

A pool of mercury '53 and a ball 54 of magnetic material plated with a mercury wettable metal are sealed within the tube 46 to rest upon the plug 50 which forms the first electrical terminal. Sealed within the smaller chamber formed within cup 47 is a ball 55 of non-magnetic electrically conducting material plated with a mercury wettable metal. The ball is of diameter greater than the diameter of hole 51 in the cup 47 so that it rests within the hole protruding below the lower surface of cup 47 and into the inside of tubing 46.

An actuator magnet 56 is positioned above the switch so that in its upper position the ball 54 of magnetic material rests in the pool of mercury in electrical contact with the first electrical terminal 50 and out of contact with the non-magnetic ball 55. The switch is then in its open position as illustrated in FIG. 9.

In its lower position the actuator magnet 56 rests against the disc 52 and is strong enough to raise the ball 54 of magnetic material to contact the non-magnetic ball 55 seated in the hole 51 of 'cup 47. On initially contacting the non-magnetic ball 55, the magnetic ball 54 is in electrical contact with the first electrical terminal 50 through the mercury pool 53, the meniscus of which has been altered upward because of the mercury wettable surface on ball 54. At this point, a momentary mercury to mercury contact is made between the first electrical terminal 50 through mercury pool 53, magnetic ball 54, and non-magnetic ball 55 to the electrically conducting walls of cup 47 which forms the second electrical terminal. At this point, the switch is momentarily closed as illustrated in FIG. 10.

Magnetic ball 54 continues up to rest against the perimeter of hole 51 pushing the non-magnetic ball 55 upwards into the chamber formed within the cup 47. At this point, the magnetic ball 54 breaks contact with the mercury pool 53 from below to break the momentary mercury contact between the electrical terminals as illustrated in FIG. 11. Upon return of the actuator magnet 56 to its upper position, the balls 54 and '55 return to their rest positions as illustrated in FIG. 9.

Another application of the present invention is the mercury tilt switch illustrated in FIG. 12 and constructed similarly to the switch illustrated in FIG. 3. Thus, a section of tubing 57 of glass or plastic is sealed at each end with cups '58 and 60 of electrically conducting metal such as alloy 52 with a coefiicient of expansion compatible with the material of the glass tubing. Cup 58 is provided with a plug 61 of mercury wettable material and cup 60 is provided with a hole 62 over which is welded a disc 63 so that plug 64 of mercury wettable material faces the inside of tubing 57. Cups 58 and 60 are heat sealed to the tubing 57. Sealed within the tubing is a mercury pool 65 and a ball 66 of material plated with a mercury wettable metal. Plug 64 and 61 of mercury wettable metal serve as the first and second electrical terminals respectively with which the electrical outlets 67 and 68 are electrically connected. Motion of the ball and mercury pool within the switch tubing as the switch is tilted first in one direction, then in another, provides momentary electrical contact between the electrical terminals.

In each of the embodiments of the invention described above, an inert dielectric fluid such as Freon may be sealed in the switch over the mercury to prevent oxidation of the mercury. Such inert fiuid would preserve the mercury absent a perfect hermetic seal at the ends of the tube by always remaining on top of the mercury surface for any orientation of the switch and without interfering with the operation. of the switch.

In the magnetic switches described above, actuation of the ball of magnetic material may also be accomplished by a solenoid wound about the tubing in lieu of the permanent magnet. Alternatively, the ball may be magnetized to form a permanent magnet, actuated by a bar of permeable material positioned over the switch for motion between an open and close position. In such an embodiment the end cups for the tubular body would be formed of non-magnetic material.

The present invention, in addition to multiple switch keyboard applications is also suitable for use in miniature electrical relays, proximity switching devices, and similar uses.

While several embodiments of this invention have een shown and described, it will be apparent that other adaptations and modifications can be made without departing from the true spirit and scope of the invention.

What is claimed is:

1. A magnetic mercury switch comprising:

an elongated container of non-magnetic, non-electrically conducting material open at each end, said container being maintained in a generally vertical position;

first sealing means providing a sealing enclosure at the bottom end of the container and including a first electrical terminal communicating electrically with the inside of the container and the outside of said first sealing enclosure, the portion of the terminal on the inside of the container having a mercury wettable surface;

second sealing means providing a sealing enclosure at the top of the container and including a second electrical terminal, the portion of the terminal on the inside of the container having a mercury wettable surface;

a pool of mercury sealed within the container and resting on the first electrical terminal;

a ball of magnetic material having a mercury wettable surface and resting in the pool of mercury whereby the mercury meniscus is altered upward along the surface of the sphere;

a permanent magnet movably positioned above said container for movement between two positions for moving the ball of magnetic material between two positions such that in one position the ball of magnetic material rests in the pool of mercury at the bottom of the container out of contact with the second electrical terminal and in the other position the ball is raised and held in contact with the second electrical terminal while contact with the mercury pool is maintained through the alteration upward of the mercury meniscus to provide a mercury to mercury contact between the two electrical terminals and means for moving the permanent magnet including:

an elongated housing open at the top end and closed at the bottom end, said housing enclosing the magnetic mercury switch axially therein and having a first electrical outlet communicating with said first electrical terminal and a second electrical outlet communicating with said second electrical terminal,

an elongated plunger positioned axially in the top of the housing above the magnetic mercury switch and in which the permanent magnet is frictionally seated, said plunger having an actuating handle extending through and in slidable relationship with the open ing in the top of the housing, and

tension means including a spring positioned axially about the plunger to maintain the plunger slidable between the said two positions by the actuating handle.

2. A magnetic mercury switch comprising:

an elongated container of non-magnetic, non-electrically conducting material open at each end, said container being maintained in a generally vertical position;

first sealing means providing a sealing enclosure at the bottom end of the container and including a first electrical terminal communicating electrically with the inside of the container and the outside of said first sealing enclosure, the portion of the terminal on vthe inside of the container having a mercury wettable surface;

second sealing means providing a sealing enclosure at the top end of the container and including a second electrical terminal, the portion of the terminal on the inside of the container having a mercury wettable surface;

a pool of mercury sealed within the container and resting on the first electrical terminal;

a ball of magnetic material having a mercury wettable surface and resting in the pool of mercury whereby the mercury meniscus is altered upward along the surface of the sphere;

a permanent magnet movably positioned above said container for movement between two positions for moving the ball of magnetic material between two positions such that in one position the ball of magnetic material rests in the pool of mercury at the bottom of the container out of contact with the second electrical terminal and in the other position the ball is raised and held in contact with the second electrical terminal while contact with the mercury pool is maintained through the alteration upward of the mercury meniscus to provide a mercury to mercury contact between the two electrical terminals; and

said first sealing means including a cup of magnetic, electrically conducting metal with coefiicient of expansion compatible with that of the container mate 'rial and having an outer surface complementary in size and shape with the inner surface of the respective open end of the container, said cup projecting into and being heat sealed in the respective end of the container whereby the permanent magnet may extend into the cup forming the first sealing means and thereby into the top end of the container in one of said two permanent magnet positions, and wherein the mercury wetting surface comprises a plug of mercury wetting metal welded to the surface of the cup on the inside of the container.

3. A magnetic mercury switch as set forth in claim 2 wherein there is provided a permanent bias magnet positioned beneath the first electrical terminal to thereby retain the ball of magnetic material against the first electrical material until raised against the second electrical terminal by the magnetic means whereby the switch is operative with its elongated axis positioned in the range from approximately to 75 from the vertical.

4. A momentary contact magnetic mercury switch comprising:

a non-magnetic, non-electrically conducting elongated container open at each end said container being maintained in a generally vertical position;

first sealing means providing a sealing enclosure at the bottom end of the container and including a first electrical terminal communicating electrically with the inside of the container and the outside of said first sealing enclosure, the portion of the terminal on the inside of the container having a mercury wettable surface;

second sealing means providing a sealing enclosure at the top end of the container including a chamber supported within the top of the container and having an opening communicating between the inside of the chamber and the inside of the container said second sealing means also including a second electrical terminal communicating with the inside of the container and the outside of the second sealing means;

a pool of mercury sealed within the container resting on the first electrical terminal;

a ball of magnetic material having a mercury wettable surface and resting in the pool of mercury at the bottom of the container and out of electrical contact with the walls of the chamber at the top of the container;

a ball of non-magnetic, electrically conducting material having a mercury wettable surface and a diameter wider than the diameter of the opening in the chamber communicating with the inside of the container, said non-magnetic ball being positioned in the chamber and resting in said opening so that a portion of the ball extends through the hole into the container; and

magnetic means for moving the magnetic ball between two positions such that in one position the ball of magnetic material rests at the bottom of the container in the pool of mercury out of contact with the second electrical terminal and the ball of non magnetic material rests in the chamber opening and such that in moving to the other position the ball of magnetic material is raised to touch the ball of nonmagnetic electrically conducting material while still maintaining contact with the pool of mercury below to thereby momentarily provide a mercury-to-mercury contact between the first and second electrical terminals, said first magnetic ball then continuing upward to the other position out of contact with the mercury pool below thereby breaking the electrical path between the first and second electrical terminals.

5. A mercury tilt switch comprising:

an elongated container of non-magnetic, non-electrically conducting material open at each end;

first sealing means providing a sealing enclosure at one end of the container and including a first electrical terminal communicating electrically with the inside of the container and the outside of said first sealing enclosure, the portion of the terminal on the inside of the container having a mercury wettable surface;

second sealing means providing a sealing enclosure at the other end of the container and including a second electrical terminal;

a pool of mercury sealed within the container and resting on the first electrical terminal; and

a ball of magnetic material having a mercury wettable surface sealed within the container to rest in the pool of mercury, one of said sealing means including a metallic member joined to said container and a metallic central portion welded to said member when said ball and said mercury are in said container.

6. A push-button switch comprising, in combination, at least one push-button movable between first and second positions for opening or closing an electric circuit, a switching assembly including an elongate container of non-magnetic, non-electrically conducting material, means sealing the opposite ends of said container, a pool of electrically conductive fluid within said container, a member of magnetic material having a surface wettable by said fluid and positioned within said container, means for magnetically controlling the position of said member in said container responsive to the position of said pushbutton, and electric circuit means connected to said switching assembly and opened or closed in accordance with the position of said magnetic member responsive to the position of said push-button, and means connecting said pushbutton to said means sealing one end of said container when said push-button is in one of said positions.

7. A keyboard assembly comprising, in combination, a plurality of keyboard keys, a switching assembly provided for each of said keys including an elongate container of non-magnetic, non-electrically conducting material, means sealing the opposite ends of said container, including at least one cup shaped member of electrically conductive magnetic material having an outer surface complementary in size to the inner surface of said container and projecting thereinto, a pool of electrically conductive fluid within said container, a member of magnetic material having a surface Wettable by said fluid and positioned Within said container, a magnet connected to each of said keys and movable from a first position spaced from a second position in contact with said cup shaped member for moving said magnetic member between operative positions out of contact and in contact with said cup shaped member responsive to operative 0 References Cited UNITED STATES PATENTS Harrison 335-56 Raettig 335205 Hunciker 33551 McCormick 335205 SiklOs 335205 Berry 335205 Marcum 33556 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner U.S. Cl. X.R. 

